Immune tolerance against infused FVIII in hemophilia A is mediated by PD-L1(+)

Authors: Tregs Becker-Gotot, J; Meissner, M; Kotov, V; Jurado-Mestre, B; Maione, A; Pannek, A; Albert, T; Flores, C; Schildberg, FA; Gleeson, PA; Reipert, BM; Oldenburg, J; Kurts, C

Affiliations: Rheinische Friedrich Wilhelms Univ, Inst Mol Med & Expt Immunol IMMEI, Venusberg Campus 1, Bonn, Germany. Univ Melbourne, Bio21 Mol Sci & Biotechnol Inst, Dept Biochem & Pharmacol, Parkville, Vic, Australia. Rheinische Friedrich Wilhelms Univ, Inst Expt Hematol & Transfus Med IHT, Venusberg Campus 1, Bonn, Germany. Univ Hosp Bonn, Clin Orthoped & Trauma Surg, Bonn, Germany. IMC Univ Appl Sci Krems, Krems, Austria. Rheinische Friedrich Wilhelms Univ, Inst Mol Med & Expt Immunol IMMEI, Venusberg Campus 1, D-53127 Bonn, North Rhine Wes, Germany.

Publication: The Journal of Clinical Investigation; 2022; 132

Abstract: A major complication of hemophilia A therapy is the development of alloantibodies (inhibitors) that neutralize intravenously administered coagulation factor VIII (FVIII). Immune tolerance induction therapy (ITI) by repetitive FVIII injection can eradicate inhibitors, and thereby reduce morbidity and treatment costs. However, ITI success is difficult to predict, and the underlying immunological mechanisms are unknown. Here, we demonstrated that immune tolerance against FVIII under nonhemophilic conditions was maintained by programmed death (PD) ligand 1-expressing (PD-L1- expressing) regulatory T cells (Tregs) that ligated PD-1 on FVIII-specific B cells, causing them to undergo apoptosis. FVIII-deficient mice injected with FVIII lacked such Tregs and developed inhibitors. Using an ITI mouse model, we found that repetitive FVIII injection induced FVIII-specific PD-L1+ Tregs and reengaged removal of inhibitor-forming B cells. We also demonstrated the existence of FVIII-specific Tregs in humans and showed that such Tregs upregulated PD-L1 in patients with hemophilia after successful ITI. Simultaneously, FVIII-specific B cells upregulated PD-1 and became killable by Tregs. In summary, we showed that PD-1-mediated B cell tolerance against FVIII operated in healthy individuals and in patients with hemophilia A without inhibitors, and that ITI reengaged this mechanism. These findings may impact monitoring of ITI success and treatment of patients with hemophilia A.